1. Field of the Invention
This invention relates to air intake control systems for diesel engines or the like and, more particularly, to such systems utilized in survival capsules and which draw air from an onboard compressed air source.
2. Description of the Prior Art
The present invention is particularly adapted for use with diesel engines installed in enclosed lifesaving vessels known as survival capsules. Such vessels have been developed as an improvement over conventional lifeboats and are particularly designed for installation and use on offshore oil well drilling platforms.
Survival capsules as presently designed are sturdy, self-propelled vessels, totally enclosed with hatches or ports for ingress and egress. These hatches can be closed and sealed against the inlet of water; and the vessel has a self-righting capability so that it can recover from a complete roll-over, as may happen in heavy seas, and still operate to carry its passengers to safety. These vessels are presently sized in ranges from 30- to 50-man capacities. Typically, the survival capsules are stored at a level just below the main deck of a well-drilling platform; and the associated survival system includes a single cable, releasable hook, and powered winch for lowering the capsule to the water and releasing it under circumstances where the need for rescue from, or abandonment of, the platform may arise.
In the environment in which survival capsules are designed for principal use, situations can develop where the capsule should be capable of operating in a flammable gas or liquid environment or, indeed, must be able to propel itself through seas covered with burning fuel. Such a situation can arise in an oil well platform disaster resulting in spillage of oil into the ocean with the possibility or existence of fire over an extended surface area. If the disaster is such that the platform must be abandoned, the capsule should have the capability of protecting its occupants from the flames on the ocean surface while propelling itself to a safe area. Systems have been developed for dealing with this problem wherein compressed air bottles are stored in the vessel for providing fresh air within the vessel at a slight positive pressure when all hatches and ports are sealed. Thus, the flames and/or noxious and possibly flammable gases in the environment surrounding the vessel are prevented from entering the capsule to the jeopardy of its occupants. A problem, however, with this system arises from the fact that the diesel engine constituting the propulsion means for the capsule draws its intake air from the interior of the capsule, thus competing with the occupants of the capsule for the use of this compressed air in sustaining life.
Diesel engines such as are employed in survival capsules of the type described have the capability of continuing to operate and develop sufficient power, even though partially starved for intake air needed for internal combustion in the engine. Although power output is degraded under such conditions, the engine is still capable of developing the power needed to drive the capsule at required speed where the intake air is temporarily restricted down to only a portion of the air normally drawn into the engine under unrestricted operating conditions.
Even greater efficiencies, however, in the allocation of the air supply to the crew and the engine are desired when breathing masks are to be employed and particularly in view of the possibility that hydrogen sulfide (H2S), an extremely poisonous gas, may be released during the drilling process.
H2S can kill humans at low concentrations (at 500 parts per million, death comes in a few minutes) and affects diesel engine performance adversely at higher concentrations (for example, at 5000 parts per million a diesel engine may begin to misfire, race, or otherwise malfunction).
Lifeboats for use in certain areas where hydrogen sulfide gas may be released from a well during the drilling process are required to carry emergency air for both the occupants of the lifeboat and for the engine which powers the lifeboat. Since diesel engines are much less sensitive to H2S than humans, and space which can be allocated to the onboard air supply is limited, it would be desirable if a technique could be devised for enabling the engine to supplement its own dedicated air supply with air exhaled by the occupants of the lifeboat.